MSc Alwin Hardenbol studied how forest structures that are important for biodiversity change over time in protected areas and under the currently prevailing conditions.
The study found that forest characteristics important for biodiversity may change quickly. For example, aspens in protected old-growth forests are rapidly declining in abundance and may lead to the disappearance of other species that are dependent on aspen trees.
“It was a surprise how quickly and synchronously these changes can occur over the whole network of protected forests. Changes in protected forests pose a major challenge on how these forests can maintain their ecological values and biodiversity”, says Hardenbol.
“Also protected areas lack natural disturbances like fires nowadays. Such disturbances may be vital to maintain diverse forests. Allowing and restoring natural disturbances in a controlled fashion on protected areas could be an effective way to maintain their diverse structure”, Hardenbol explains.
Forest growth and succession are well-known phenomena in the managed Finnish forests but much less is known about how these changes affect the biodiversity and conservation value of protected forests. In particular, several small-scale or rare structures that maintain specialised species are very prone to changes.
For example, the presence of very old broadleaved trees in a forest can substantially improve a local forest’s biodiversity because they host a large number of other species. Similarly, tree cavities that are often found in broadleaved trees can provide a home for multiple species, especially birds and mammals. But both broadleaved trees and their cavities can quickly change.
Hardenbol investigated how broadleaved trees and structures associated with these trees can change in their abundance over time through long-term monitoring of 16-30 years. He also examined what factors may affect the growth and survival of these species.
Old aspen trees were monitored in a network of 15 protected areas. Results showed that the density of aspen declined by 37 % during the study period of 18 years. At the same time, recruitment of young trees was uncommon if no disturbances occurred. Noteworthy, these changes took place synchronously in all studied sites. The results show that protected areas may quickly lose some of their characteristics important for biodiversity.
Hardenbol also studied how specific within-tree characteristics can alter over time. For this purpose, he studied what factors affect the persistence of tree cavities excavated by Three-toed Woodpeckers using data from a 30-year period. Results showed that the cavities had a median lifespan of 10 years. Characteristics of cavity trees had a particularly strong influence on persistence. Cavities lasted longer and provided nesting places for other birds in coniferous, healthy, and larger trees. However, for aspen, in which cavities are common, cavities in small trees also persisted a long time.
Finally, he investigated the factors that affect the survival of young broadleaved trees in managed and protected forests. Results show that mimicking natural disturbances like fire can promote broadleaved trees. Browsing by moose and hares effectively limits the opportunity for broadleaved trees to grow in young forests. However, the results also showed that controlled use of fire was highly effective at reducing browsing.
The doctoral dissertation of MSc Alwin Hardenbol, entitled Dynamics of biodiversity-rich deciduous trees and microhabitats in boreal forests will be examined at the Faculty of Science and Forestry on the 16th of December in Joensuu. The opponent in the public examination will be Docent, Dr. Sci. Atte Komonen, University of Jyväskylä, and the custos will be Professor Jari Kouki, University of Eastern Finland. The public examination will be held in English.
